Selection of Antagonistic Bacteria of Clavibacter michiganensis subsp. michiganensis and Evaluation of Their Efficiency Against Bacterial Canker of Tomato

Authors:
  • MFM. Fatmi
    M. Fatmi
  • EBE. Benizri
    E. Benizri
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Abstract
A 178 bacterial strains, antagonistic towards Clavibacter michiganensis subsp. michiganensis , the causal agent of bacterial canker of tomato, were isolated from bulk soil, the rhizosphere and rhizoplane of tomato, originating from different sites in the Souss-Massa Valley, Agadir, Morocco. The strains were characterized on the basis of the Gram stain, sporulation, fluorescence on King's B medium and physiological tests. All of the strains inhibited C. m. subsp. michiganensis on nutrient-broth yeast extract agar (NBYA), with zones of inhibition ranging from 2-30 mm. The most efficient strains were Gram-negative and most of these were fluorescent pseudomonads. Twenty-four strains (ampicillin and nalidixic acid resistant mutants) were selected for their ability to colonize tomato roots. Less than a third (7/24) completely colonized the roots of all the seedlings. Only six strains colonized the main and lateral roots of 50% of the seedlings, and eleven colonized < 50% of the seedlings. The best root-colonizing strains were fluorescent pseudomonads. Eighteen strains were screened in greenhouse pot experiments for control of bacterial canker. Only three of the 18 strains reduced infection when applied as a seed treatment compared to the untreated control. The majority of the strains reduced the infection totally when applied as a seed treatment followed by a root treatment before transplanting compared to the control. This combined treatment was significantly more efficient than the seed treatment alone.

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